There are many types of compact discs, and the method and apparatus according to the invention for repairing a damaged compact disc is suitable for repairing damage to substantially all types of compact discs. For example, one type of compact disc is a compact disc record on which audio material is recorded, for example, music. Another type of compact disc is a CD ROM on which data is recorded for use in a computer. A further type of compact disc is one on which video signals are recorded. In all such compact discs the signals recorded on a compact disc are recorded in digital form. Typically, a compact disc comprises a recordable layer onto one surface of which the digital signals are recorded. A reflective layer, typically an aluminium coating is vacuum coated onto the surface of the recordable layer on which the digital signals are recorded for reflecting laser light from the surface of the recordable layer on which the digital signals are recorded. A layer of lacquer is provided over the reflective layer for protecting the reflective layer. The recordable layer typically, is of a polycarbonate material, and defines a reading surface through which laser light is passed to the reflective surface of the recordable layer, and from which reflected laser light from the reflective surface passes for facilitating reading of the digitally recorded data.
Such compact discs are susceptible to two types of damage, both of which, are caused by scratches on the disc. One type of damage results from scratches on the lacquer and reflective layers. Where such damage occurs, in general, the compact disc is damaged beyond repair. The other type of damage is caused by scratches on the reading surface of the recordable layer. Scratches on the reading surface, in general, cause the laser light being directed to the recorded reflective surface to be refracted away from the data track to which it is directed, or alternatively, such scratches may cause the reflected laser light from the reflective surface to be refracted to the extent that it is undetectable by a reading head which is reading the data from the recordable layer. Provided the scratches on the reading surface are not excessively deep, in general, it is possible to remove the scratches to an extent that the compact disc is again useable. In general, damage caused by scratches on the reading surface which extend in a generally radial direction relative to the compact disc do not prevent reading of the compact disc. However, scratches which extend circumferentially relative to the compact disc, or tangentially to a circumference of the compact disc cause serious problems, particularly, where such scratches extend along an arc of reasonable length along a digitally recorded track of the compact disc.
U.S. Pat. No. 5,099,618 addresses the problem of repairing damage caused by scratches on the reading surface of the recordable layer of a compact disc. The U.S. specification discloses apparatus for repairing the damage, which comprises a rotatable disc carrier on which the damaged compact disc is supported, and a rotatably mounted abrasive disc carrying shaft which is disposed and moveable relative to the disc carrier for rotating and moving a series of abrasive discs radially relative to the compact disc for abrading the reading surface of the compact disc for removing a scratch. The U.S. specification discloses a method for using the apparatus for abrading the reading surface of the compact disc which requires that the reading surface should be subjected sequentially to a plurality of abrading treatments with abrading discs of decreasing coarseness. The method requires commencing abrading of the reading surface with the most coarse abrading disc and finishing with an abrading disc or abrading paste of least coarseness. While the method and apparatus disclosed in U.S. Pat. No. 5,099,618 does remove material from the reading surface of the compact disc to the extent that, in general, the scratch does not affect playing or use of the compact disc, it suffers from a serious disadvantage in that in many cases significantly more material is removed from the reading surface of the compact disc than is necessary. This can in many cases have a harmful effect on the compact disc, to the extent that where the depth of the protective layer is reduced below a certain minimum depth, due to refraction of either the laser light incident on the reading surface or the reflected light therefrom, reading of the digitally recorded data on the recordable layer is no longer possible.
There is therefore a need for a method for repairing a damaged compact disc for rendering the compact disc useable which overcomes this problem.